Does GJ 3473 b possess a substantial atmosphere?

Determine whether the rocky exoplanet GJ 3473 b possesses a substantial atmosphere by resolving the current degeneracy between atmospheric and bare-rock interpretations of its JWST/MIRI F1500W secondary eclipse measurement.

Background

The authors observed four JWST/MIRI F1500W secondary eclipses of GJ 3473 b and measured an average eclipse depth of 186±45 ppm, corresponding to a brightness temperature of 820±120 K. Forward modeling shows that both airless surfaces (spanning varied compositions, textures, and space weathering states) and idealized atmospheres (e.g., CO2 or H2O over a range of surface pressures) can reproduce the observed depth.

While thick CO2 atmospheres are disfavored (95% credible upper limit of 1.2–6.5 bar), the data remain consistent with thin atmospheres and a range of bare-rock scenarios. Additional spectroscopic or phase-curve observations are required to break these degeneracies and definitively establish the presence or absence of an atmosphere on GJ 3473 b.

References

The presence or absence of an atmosphere on GJ 3473 b remains an open question, as the measured eclipse depth is consistent with both a bare rock surface and a secondary atmosphere.

— Hot Rocks Survey V: Secondary Eclipse Photometry of GJ 3473 b with JWST/MIRI  (2604.02332 - Holmberg et al., 2 Apr 2026) in Section 6: Conclusions